Some of the most challenging tasks for current Traction Control (TC) systems include situations where a vehicle is “stuck” in (deep) snow or mud, or on a possibly icy and/or inclined road.
One approach to vehicle traction control in non-moving conditions is described in U.S. Pat. No. 5,265,693. In this example, higher slip may be used if controller senses a non-moving (stuck) vehicle. In another approach, (U.S. Pat. No. 5,735,362), the controller uses a combination of a controlled increase in target wheel slip and subsequent phases that reduces driving power and torque to the wheels.
However, the inventors herein have recognized potential issues with such approaches. For example, the use of solely higher slip may actually cause the vehicle to become more entrenched and reduce the ability of the operator to move the vehicle. Also, in continuing traction control intervention that still may not move the vehicle, the operator may become frustrated to the point of turning the traction control system off, and trying to negotiate the situation without traction control active. These issues may lead to decreased customer satisfaction.
In one approach, a method for controlling a powertrain of a vehicle with wheels, the vehicle having a pedal actuated by a driver, is described. The method comprises:
generating powertrain torque transmitted to the wheels in a first relation to actuation of the pedal by the driver during a first condition where said transmitted torque causes said wheels to slip relative to a surface;
overriding said driver actuated powertrain torque to control said slip; and
during a second condition after said first condition where said vehicle is moving less than a threshold, generating powertrain torque transmitted to the wheels in a second relation to actuation of the pedal by the driver, where for a given pedal position, less powertrain torque is transmitted with said second relation compared to said first relation.
In this way, if overriding driver actuation to perform traction control still results in a non-moving vehicle condition, for example, the traction management system can return control to the driver, but with finer resolution at lower torques to better navigate the condition. In other words, in one example, the vehicle's powertrain response behavior to a command input may be modified if a non-moving condition is identified in order to provide the driver higher resolution powertrain torque output control. In this way, improved vehicle performance may be achieved, and improved customer satisfaction obtained.
In one example, once the vehicle is moving a sufficient amount, the vehicle vehicle's powertrain response behavior can be returned to that which corresponds to a moving vehicle. This transition may be gradual, in one example, so that driver perception of the transition may be reduced.
Note that various types of relations may be used, such as linear or non-linear, for example. Further, the relations may be a function of various other parameters, such as, for example, transmission gear state, temperature, or others.